Senile dementia caused by Alzheimer's disease has raised a serious social problem, and the early establishment of diagnoses and therapeutic methods of Alzheimer's disease has been desired. As lesion characteristic of the brains of patients with Alzheimer's disease, the excessive formation of senile plaques and neurofibrillary tangles have been known. Of these, one of the main constituents of the senile plaque is a .beta.-amyloid or a derivative thereof.
The .beta.-amyloid is a peptide composed of about 40 amino acids, and is coded in the vicinity of the transmembrane region of an amyloid precursor protein (hereinafter referred to as an APP). Amino acid sequences of the .beta.-amyloids are shown below:
.beta.-Amyloid (1-38)! SEQ ID NO: 1
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y
.beta.-Amyloid (1-39)! SEQ ID NO: 2
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y-Val
.beta.-Amyloid (1-40)! SEQ ID NO: 3
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y-Val-Val
.beta.-Amyloid (1-41)! SEQ ID NO: 4
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y-Val-Val-Ile
.beta.-Amyloid (1-42)! SEQ ID NO: 5
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y-Val-Val-Ile-Ala
.beta.-Amyloid (1-43)! SEQ ID NO: 6
Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe -Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gl y-Val-val-Ile-Ala-Thr
According to recent reports, some of the patients with familial Alzheimer's disease belong to families having point mutations on APP, and the possibility has been pointed out that the .beta.-amyloids are one of the causative substances for Alzheimer's disease. Based on such a background, the .beta.-amyloids have been intensively studied as a main subject for the investigation of Alzheimer's disease, and various results of the studies have been presented.
However, assay systems for detecting the .beta.-amyloids easily and with high sensitivity have hitherto been scarcely reported, although deep interest has been expressed in the .beta.-amyloids. The sandwich enzyme immunoassay of the .beta.-amyloids is only reported by P. Seubert et al., Nature, 359, 325-327 (1992)!.
The assay system of P. Seubert et al. is reported to have a detection sensitivity of 100 pg/ml, which is not satisfactory. Further, the assay system is reported to react also with a partial peptide consisting of N-terminal 28 residues hereinafter refereed to as .beta.-amyloid (1-28)!. However, a number of hydrophobic amino acids exist in C-terminal portions of the .beta.-amyloids, .beta.-amyloid (29-39), .beta.-amyloid (29-40), .beta.-amyloid (29-41), .beta.-amyloid (29-42) or .beta.-amyloid (29-43). This C-terminal region is therefore considered to be embedded in a cell membrane, and is assumed to play an important role in aggregation and deposition of peptides. For this reason, it is important to quantify .beta.-amyloids having the C-terminal hydrophobic regions. However, the above-mentioned assay system of P. Seubert et al. does not satisfy the social demands in the specificity and sensitivity.
Usually, antibodies to peptides are prepared by immunizing complexes of the peptides and natural or synthetic polymer carriers. Also in the case of the .beta.-amyloids, the report of P. Seubert et al. described above shows that antibodies reactive to .beta.-amyloid (1-40) can be prepared using N-terminal portions of the .beta.-amyloids which are hydrophilic regions, for example, .beta.-amyloid (1-16), as immunogens. However, it is not clear whether or not an antibody to the C-terminal portion of the .beta.-amyloid which is the hydrophobic region embedded in the cell membrane can be prepared by usual methods. Further, even if the antibody to such a region can be obtained, it does not provide an assurance at all that it reacts with the .beta.-amyloid. Furthermore, if the antibody only shows an extremely low affinity for the .beta.-amyloid, it is generally difficult to expect that, for example, the above-mentioned sandwich enzyme immunoassay of P. Seubert et al. can be established with the antibody. Namely, although various antibodies have hitherto been prepared for the purpose of detecting the .beta.-amyloids, there is no report that the antibody to the C-terminal portion of the .beta.-amyloid has been prepared and applied to the sandwich enzyme immunoassay, thereby developing an immunoassay by which the .beta.-amyloid can be detected with high sensitivity and specificity without cross reaction with .beta.-amyloid (1-28). It is further reported that .beta.-amyloid (25-35) has homology to tachykinin in its amino acid sequence, and has cytotoxicity B. A. Yankner et al., Science, 250, 279-282 (1990)!. However, there is no report at all that an antibody to .beta.-amyloid (25-35) has been prepared and applied to the sandwich enzyme immunoassay, thereby developing an immunoassay by which the .beta.-amyloid can be detected with high sensitivity and specificity without cross reaction with .beta.-amyloid (1-28).
Recently, it is further reported that, of the .beta.-amyloids, .beta.-amyloid (1-42) is mainly deposited in the cerebral cortex (senile plaques), whereas .beta.-amyloid (1-40) is mainly deposited in the cerebral blood vessel (angiopathy) Arch. Biochem. Biophys., 301, 41-53 (1993)!. It is further suggested that the seed formation of C-terminal portion-containing peptides such as .beta.-amyloid (1-42), .beta.-amyloid (26-42), .beta.-amyloid (26-43) and .beta.-amyloid (34-42) causes the deposition of water-soluble .beta.-amyloid (1-40) Biochemistry, 32, 4693-4697 (1993)!. From such reports, the difference in the deposition manner between .beta.-amyloid (1-40) and .beta.-amyloid (1-42) is considered to be largely related to Alzheimer's disease. When Alzheimer's disease is diagnosed, therefore, sensitive and discriminative determination of .beta.-amyloid (1-40) and .beta.-amyloid (1-42) is important. However, suitable antibodies for this purpose have not been reported yet.
An object of the present invention is to provide a novel antibody which can sensitively, specifically determine a .beta.-amyloid having a C-terminal hydrophobic region or a derivative thereof, preferably a monoclonal antibody. Another object of the present invention is to provide a method for assaying a .beta.-amyloid or a derivative thereof with the antibody.